How do you have challenging content? Its one thing that's concerning me.
The healer / tank dcing is one thing that dynamic events will get rid of and I know what you mean -- that it sucks when you have a group full of derps who aren't communicating, but how do you have difficult content?
These people aren't just going to go away, they're going to by faux cooperating with you, 'im in ur dynamic event' style. Stupid people arent even the worst, what about people afking dynamic events or botting and not contributing but also inflating the scaling.
Hoping dungeons and explorable modes are solid, there are a punch of potential balance issues, but that probably isn't even worth speculating over at this point.
Consider that failure is actually a valid option in GW2; basically, failing leads to its own events, so in a way, they're allowed to make it harder than something like RIFT (at least in later zones), otherwise we'd miss half the content.
I think ANet have a system that excludes AFK's from affecting the scaling. Now botting, I don't know how that will be dealt with.
Just reading a review and it said the quests ate split between "tasks" and "events". Tasks are bog standard mmo quest fare you pick up from someone the events are the in world stuff they always bang on about (having never mentioned tasks anywhere On their webbie just events) it would be interesting to know a break down of how many quests are tasks and how many are events.
Honestly, that's just terminology utilised by the reviewer on the spot. The quests are all events, but there are separate types of events.
Elite events = Require a whole bunch of people and are supposed to be pretty damn hard. Quantity wise, it would seem that the endgame zones (Orr) apparently are full of pretty much elite events.
Meta-events = Something new it would seem, these tell the "story" of a zone and can cover up to a quarter of a zone alone. Typically larger than your standard event.
Events = Ran out of words

These tend to be smaller than meta events and consist of tug-of-war style of gameplay it would seem, e.g pirate invasion pushing them back and forth across a chain until some resolution is reached.
Renown events = These are probably the "tasks" mentioned. These are static things that change over time; you may be feeding some cows on a farm earlier, go out to do some other more interesting events, come back and the whole bloody place is alight with bandits attacking. Completing these allows you access to special vendors. These seem to be generally the "lazy-mode" stuff, for when people can't be asked to explore or run around looking for events. As a result, they tend to be the least interesting of the events, I'm assuming so people don't merely play these. I believe someone found a number somewhere of 200-odd renown events.